Size- and shape-dependent separation of TiO2 colloidal sub-populations with gravitational field flow fractionation

The simplest field flow fractionation technique, which uses the earth's gra vity as the external field is applied to isolate two populations, which dif fer in both shape and size, from a polydisperse sub-micron TiO2 powder of h omogenous density. The fraction eluted first is spherical with an average d iameter of 0.31 mum while the second fraction is ellipsoidal and can be ass ociated with a 0.45 mum hydrodynamic diameter. Elution conditions appeared to be very sensitive to electrolyte and surfactant characteristics in the c arrier phase as well as on the sample concentration. Using 25 mul (1%, w/w) sample suspension, separations of spherical from ovoid particles was perfo rmed in almost 2 h with a mobile phase of 0.001 M KNO3-0.01% (v/v) F1-70 in water in a 0.025-cm thick channel made of polystyrene walls. (C) 2001 Else vier Science B.V. All rights reserved.